Wireless technologies have seen significant improvement over the past several years. All sorts of communications devices are now seen as potential candidates for the installation of a wireless communications device. From telephones, to computers, to personal digital assistants, the list of wireless devices grows everyday. As merely an example, Bluetooth wireless local area networks purport to enable the installation of wireless devices into everything from jewelry to major appliances.
The Institute of Electrical and Electronics Engineers (IEEE) has developed new wireless ethernet standards under 802.11, which includes IEEE 802.11a, some of which have begun gaining acceptance in the industry. Even further, the European Telecommunications Standards Institute (ETSI) has developed a high performance radio local area network (HiperLAN). HiperLAN has an embodiment called HiperLAN/2, which is seen as being in direct competition for the widespread acceptance of the IEEE 802.11a standard. Both transmit in the 5 GHz unlicensed national information infrastructure (UNII) frequency range, and have data rates of about 54 Mbps, and share other similarities at the physical layer. For example, both standards use orthogonal frequency division multiplexing. This means that the design of the radio architecture in both systems can have certain commonalities.
These commonalities are fortunate, because as transmission frequencies and data transfer rates rise, the complexity of the underlying radio architecture necessarily rises. The 802.11a and HiperLAN standards require especially complex solutions for the standards to be met. These complex solutions increase cost, which in turn increases the time needed to gain widespread acceptance in the industry.
Regular transceiver architectures employing I/Q down-converters cause problems in orthogonal frequency division multiplexing (OFDM) because they produce I/Q imbalance and DC offset, whereas this particular OFDM requires these values to be extremely low in order to obtain the specified signal to noise ratio (SNR). Intermediate frequency (IF) sampling architectures solve these problems, but introduce problems of their own, such as higher conversion speed causing increased analog-digital converter power consumption, and higher required selectivity to avoid both aliasing and image leakage. The higher selectivity requirement usually leads to using two intermediate frequency-surface acoustic wave (SAW) filters. These filters however, lead to increased noise figure and higher cost. Thus, an unaddressed need exists in the industry for an IF sampling architecture that obviates these problems.